1. Field of the Invention
This invention relates to cannon-launched projectiles. More particularly, this invention relates to an apparatus and method for scanning a target area to select a target located therein and for providing target position information to the guidance system of the projectile to guide the projectile to impact the selected target.
2. Description of the Prior Art
It is well-known that a cannon-launched projectile is a projectile which is launched from a cannon by means of an explosive charge. It is also well-known that the anticipated trajectory of the projectile when launched can be fairly well calculated. This enables the gunner to fire the projectiles to impact a pre-selected target area with reasonable consistency.
Obviously, one of the major disadvantages to the cannon-launched projectile is the inability to control the flight of the projectile after the projectile is launched. One major advancement in this art has been the discovery that fins could be incorporated within the projectile which, after launching, would move from a retracted position in the projectile to an extended position. Usually, the fins are configured to controllably spin the projectile during flight. It was soon found that the spinning projectile is indeed more stable during flight, thereby increasing the accuracy of the projectiles in impacting the target area. Although these significant advancements have been made, there still exists a great need in the industry to be able to control the flight of the projectile after launching, so as to locate and then impact a particular target.
Heretofore, the use of radar techniques incorporated within the projectile have been unsuccessful. The primary reasons for the inability to incorporate a radar in the projectile has been the enormous acceleration (typically 170,000 m/s.sup.2) to which the projectile is exposed during the launch. It is, therefore, difficult for any type of moving mechanical device incorporated within the projectile to survive the launch. Thus, any type of state-of-the-art scanning or tracking radar, such as those that utilize sequential lobing, conical scan, or simultaneous lobing or monopulse, requires the use of an oscillatory or rotating antenna or feed horn to transmit and receive a radar beam for locating a potential target and computing an error signal representative of the locating of the target. Obviously, any type of oscillating or rotating antenna or feedhorn would have difficulties to survive a launch.
Another difficulty that is inherent in such state-of-the-art radars, that have been discussed for cannon launched projectiles, is that radar echoes are obtained from such a large area on the ground that the ground clutter echoes will be more powerful than the echo from a potential target, which subtends only a very small part of the area covered by the radar radiation.
Another primary disadvantage to present thoughts about cannon-launched projectiles is the inability to hit a moving target which requires that an inertial reference can be established. It is well-known in the art of missile guidance that in order to hit a moving target, it is necessary to use a proportional navigating guidance system. This requires the inertial rate of the line of sight vector to be determined which, of cource, can not be performed without an inertial reference.
For the reasons stated above, mechanical state-of-the-art gyroscopes are unsuitable to establish the required inertial reference due to the fact that such mechanical gyros would not survive the enormous acceleration of the launch. Although there exists some potential to track the clutter background of the target area to establish a fixed reference directly from the ground, such a procedure would accurately establish an inertial reference only with respect to very limited types of clutter backgrounds. Accordingly, not only has there been a failure to overcome the problem of scanning, there also exists the significant problem of establishing an inertial reference for use during the tracking of a moving target.
Therefore, it is an object of this invention to provide an apparatus and method which overcomes the aforementioned inadequacies of the prior art devices and provides an improvement which is a significant contribution to the cannon-launched projectile art.
Another object of this invention is to provide an apparatus and method for controlling the flight of a cannon-launched projectile after the projectile is launched.
Another object of this invention is to provide an apparatus and method for controlling the flight of the cannon-launched projectile with sufficient ruggedness to survive the enormous acceleration of the projectile during the launch.
Another object of this invention is to provide an apparatus and method to detect a target that subtends only over a very small part of the area covered by the radiation from the radar transmitter.
Another object of this invention is to provide an apparatus and method for controlling the flight of the cannon-launched projectile to impact a selected target located within a predetermined target area.
Another object of this invention is to provide an apparatus and method for controlling the flight of a cannon-launched projectile to scan the target area to select a potential target, track the selected target if moving, and then alter the trajectory of the projectile to impact the selected target.
Another object of this invention is to provide an apparatus and method for controlling the flight of a cannon-launched projectile which utilizes rate gyro means which are sufficiently hard to withstand the acceleration of the launch to establish the inertial reference needed for tracking a moving selected target.
The foregoing has outlined some of the more pertinent objects of the invention. These objects should be construed to be merely illustrative of some of the more prominent features and applications of the intended invention. Many other beneficial results can be attained by applying the disclosed invention in a different manner or modifying the invention within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the invention may be had by referring to the summary of the invention and the detailed description describing one preferred embodiment in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.